Authorship and Audience
The author of Esther is unknown. Based on the author's knowledge of Susa, Persian customs, and the emphasis/explanation of the Jewish festival of Purim, the author was likely a Jew who lived or had lived in Persia. The author was writing to other Jews to explain the significance of the celebration of Purim.
Date and Historical Context
There are a couple important dates that frame the dating of the book of Esther. First, the reign of Xerxes, the king described in Esther, ends in 465 BC. Ezra 10:2 refers to Xerxes' rule in the past tense which implies that the book was written after 465 BC.1 Second, the Persian empire would finally succumb to the Greeks in 331 BC. As there are no hints of Greek influence in the book(todo: add footnote here), it was likely finished before this date. Thus, Esther was likely written between 465 and 331 BC.
0. Introduction 
A. Introduction to Xerxes and his Party [1:1-9]
B. The King's Request and Vashti's Refusal [1:10-12]
C. The King's Response [1:13-22]
I. The King Searches and Chooses Esther as the New Queen [2:1-20]
II. Mordecai Saves the King [2:21-23]
III. Haman's Plot to Kill the Jews 
IV. Esther Receives News of Haman's Plot and Decides to Intercede 
VI. Esther's First Banquet [5:1-8]
VII. Haman's Plot to Kill Mordecai [5:9-14]
VIII. Haman Honors Mordecai Rather Than Killing Him 
IX. Esther's Second Banquet Results in Haman's Death 
X. Mordecai Made Second in Command and Jews Allowed to Defend Themselves and Attack Their Enemies 
XI. Jews Destroy Their Enemies [9:1-19]
XII. Epilogue [9:20 - 10:3]
A. Festival of Purim Instituted [9:20-32]
B. Mordecai's Greatness 
God's sovereignty (even over sinful people and circumstances). One of the most ironic aspects of the book of Esther is that God's name is no explicitly mentioned and yet one of the principle themes is the sovereignty of God. This is evidenced by the numerous 'coincidences' and ironic twists in the story. Haman, enemy of God's chosen people, is thwarted, no thanks to the drunken king Xerxes, and ends up being killed on the very apparatus he created for the death of Mordecai. The fact that God is never mentioned is actually meant to encourage the reader to look 'behind' the circumstances and notice that there is more going on than meets the eye. The festival of Purim itself is an acknowledgment that God is sovereign even over chance and probability.
This should be encouraging to us, as Christians, in at least two ways. First, we live a fallen sinful world that is largely beyond our control. It is easy to get discouraged by the injustices and tragedies that plague our fallen world, but Esther is a reminder that God, although He may appear absent, is still in control. Second, Esther ought to encourage us because we ourselves are sinful. Will our sins undo God's plans? Can our unfaithfulness derail God's purpose? Esther is a reminder that God uses even sinful people, like us, with a little faith (see Esther 4:13-17) to accomplish His plans. To be clear, this is not license or excuse for sin, but ought to be comforting as we battle sin in this life.
- Human action in the plans of a sovereign God. Esther emphasizes the importance of human action in the God's plans. God appoints ends and also the means to achieve those ends. God's sovereignty does not excuse our laziness or apathy. We see this clearly from Mordecai's comments in Esther 4:13-14 as he admonishes Esther to act, even at the risk of her own life. Mordecai is convinced that God will save His people and understands that God may use human means to do so. Take a second to think about the impact and force of this truth. The book of Esther is establishing that God is sovereign over everything large and small, holy and sinful. It simultaneously establishes the importance of human action and decision; not because it is powerful on its own, but because there is a sovereign God working through it behind the scenes. In the book of Esther, God's sovereignty is closely tied with a call to be faithful and courageous.
The book of Esther is a Chiasm. A chiasm, also called a chiasmus or chiastic structure, is a common literary device throughout the Bible where the first and last sections of a passage are similar/balanced, the second and second-to-last sections are similar/balanced, the third and third-to-last sections are similar/balanced, and on and on leading to a central, focal point in the passage. This gives the narrative a balance, provides artistic unity to a work, and focuses the readers attention to the focal point. In the book of Esther, the chiasm contrasts Haman and Mordecai with the focal point being the time when Haman leads Mordecai around on a donkey. The point of this dramatic reversal is that it could only happen if there was something other than 'chance' at work. In the book of Esther, the chiasm also serves to accentuate the structure and balance of the events which is yet another way to highlight the fact that God is at work in the events described in the book. If you were to outline the chiastic structure of the book, it would look something like:
A. Xerxes's Leadership - 1
B. Haman Promoted - 3:1-6
C. Haman's Plot to Destory the Jews - 3:7-14
D. Esther's 1st Banquet (result: Haman Plans to Hang Mordecai) - 5
E. Haman Honors Mordecai - 6
D'. Esther's 2nd Banquet (result: Haman is Hung) - 7
C'. Mordecai's Plot to Save the Jews - 8:8-17
B'. Mordecai Promoted - 8:1-7
A'. Mordecai's Leadership - 10
1. "Esther," Grace to You, August 18, 2016, accessed February 15, 2018, https://www.gty.org/library/bible-introductions/MSB17.